1. Field of the Invention
The present invention relates to a color ink jet recording method capable of recording a color image clearly and at high density, and particularly to a color ink jet recording method using color ink materials in yellow (Y), magenta (M) and cyan (C), or green (G), red (R) and blue (B) or the like, and black ink (Bk).
2. Related Background Art
An ink jet recording method is used in printers, copying machines, facsimile equipment and the like for the reasons such as low voice, low running cost, easy down-sizing, and easy color recording.
Normally, a color ink jet recording method uses three color ink materials, cyan, magenta and yellow, and in addition to them, black ink for color recording.
Conventional ink jet recording methods required using dedicated paper having an ink absorbing layer in order to obtain a color image in high color development without feathering or bleeding. In recent years, due to an improvement of ink, ink jet recording methods having a good aptitude for printing on "plain paper", which is used in large volume with printers, copying machines and the like, have been put to a practical use. However, under the present situation, the quality of printing on "plain paper" still remains at an unsatisfactory level. A primary factor for this is said to be difficulty in attaining both less ink bleeding between colors and good recording quality in black (particularly recording quality of black characters).
Usually, for recording a color image on plain paper by an ink jet recording method, quick drying ink featuring a high speed of penetration into plain paper is used. As a result, a high quality image without ink bleeding between colors is obtained. However, density is lower as a whole, and the ink tends to finely feather along fibers of paper around the recorded image area of each color, i.e. so-called feathering tends to take place.
Feathering is relatively less marked in a color image area, but is more likely to be marked in a black image area with a resultant deterioration in recording quality. In particular, when a black image is a character, a blurred character without sharpness will result, and hence the recording quality will be poor.
To obtain high quality black recording with less feathering and higher density, it is necessary to use black ink, which is relatively low in the speed of penetration into plain paper. In this case, however, each color ink bleeds at the boundary between recorded image areas in black and each color with a resultant marked damage to the recording quality.
Thus, contrary problems are involved in improving the color recording quality, i.e, prevention of the ink bleeding between black and colors and reduction of the feathering particularly of black ink in a compatible manner.
Accordingly, a recording method wherein recording is not made in an area along the boundary between black and color is proposed in Japanese Patent Application Laid-Open No. 3-146355. This method, however, has a drawback that data to be recorded changes.
Also, a recording method which uses a multi-color head for color recording and a character recording head and selects either one according to a record image is proposed in Japanese Patent Application Laid-Open No. 4-158049. This method, however, requires the character recording head in addition to the conventional color recording multi-color head with a resultant increase of cost and equipment size.
In the specification of Japanese Patent Application Nos. 4-205548 and 4-293022 filed by the applicant (now Japanese Laid-Open Patent Application Nos. 6-47927 and 6-87222, respectively), proposed is a method of preventing bleeding in the boundary between black and color by superimposing color ink materials to form a black area along the boundary between black and color. Thus produced black by using color ink materials is called PCBk (Process Color Bk). This method involves a problem of color tone in a black portion formed with color ink and a portion formed by mixing black and color at a certain rate.
On the other hand, also devised is a method wherein multi-pass printing is conducted in an area along the boundary between black and color to complete printing by a plurality of scans, thereby allowing previously applied ink to sufficiently fix and thus preventing bleeding in the boundary between black and color. Due to multi-pass printing, this method takes a longer printing time as compared with normal printing (1-pass printing) wherein printing is completed by one scan.
In multi-pass printing above, the more the scanning count increases, the longer the printing time becomes, and hence a longer time can be taken for fixing with a resultant good effect against bleeding. However, a printing speed drops. Thus, the ink configuration above brings a high quality image with good recording quality in black and no bleeding between colors, but sacrifices the printing speed. The printing speed is a very important parameter for recording apparatus, and hence it is a problem to solve for color ink jet recording apparatus to attain both high quality image and higher printing speed.